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Unix Version 7 - man page for rf (v7 section 4)

RF(4)					       Kernel Interfaces Manual 					RF(4)

rf - RF11/RS11 fixed-head disk file
This file refers to the concatenation of all RS-11 disks. Each disk contains 1024 256-word blocks. The length of the combined RF file is 1024x(minor+1) blocks. That is minor device zero is taken to be 1024 blocks long; minor device one is 2048, etc. The rf0 file accesses the disk via the system's normal buffering mechanism and may be read and written without regard to physical disk records. There is also a `raw' interface which provides for direct transmission between the disk and the user's read or write buffer. A single read or write call results in exactly one I/O operation and therefore raw I/O is considerably more efficient when many words are transmitted. The name of the raw RF file is rrf0. The same minor device considerations hold for the raw interface as for the normal interface. In raw I/O the buffer must begin on a word boundary, and counts should be a multiple of 512 bytes (a disk block). Likewise seek calls should specify a multiple of 512 bytes.
/dev/rf0, /dev/rrf0
The 512-byte restrictions on the raw device are not physically necessary, but are still imposed. RF(4)

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